NEW YORK (Reuters Health) - A single dose of the BCG vaccine appears to provide protection against tuberculosis for 50 to 60 years, according to a report published in the May 5th issue of the Journal of the American Medical Association.

Despite being in use for more than 80 years, the long-term efficacy of the BCG vaccine has not been known, lead author Dr. Naomi E. Aronson, from the Uniformed Services University of the Health Sciences in Bethesda, Maryland, and colleagues note.

The new findings are based on a study of American Indians and Alaska Natives who were given the BCG vaccine or placebo in the late 1930s and followed through 1998. A total of 1483 subjects received the vaccine and 1309 were given placebo.

The incidence of TB in the vaccine group was 66 cases per 100,000 person years, much lower than the rate seen in the control group--138 cases per 100,000 person-years, the authors note.

This translates into a vaccine efficacy of 52%, which remained stable after accounting for a variety of factors, such as age at vaccination, subsequent BCG vaccination, and BCG strain.

A slight non-significant decrease in vaccine efficacy was noted over time, which was more apparent in men than in women, the researchers point out.

"This placebo-controlled trial of BCG vaccine is the only study, to our knowledge, to demonstrate that its vaccine strains conferred a considerable degree of protection throughout most of the 60-year follow-up period," the authors state.

"These results should provide encouragement to investigators aspiring to produce a vaccine with similar or improved characteristics."